Replace kvin URIs with namespaced URLs

[VladimirAlexiev]

(Split from PR #32 that should be rejected.)
kvin is not a registered URI scheme so it is bad style to use it for ontology terms.

@kenwenzel points out that some platforms use such a practice, eg jdbc, odbc, app, slack, msteams etc. But they need to enact (locally "resolve") these URIs to do some actions.

For RDF data, it's better to use (prefixed) URLs.

Define a prefix for a namespace like http://linkedfactory.github.io/vocab/kvin/ (or http://linkedfactory.github.io/vocab/ may be better),
then we can write kvin:something that denotes a URL,
rather than <kvin:something> that is a URN using an undefined scheme.